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Re: Grounding Choreographies (the atoms) - WAS Simple Choreography composition suggestion

From: Frank McCabe <frankmccabe@mac.com>
Date: Thu, 17 Jul 2003 19:23:18 -0700
Cc: Martin Chapman <martin.chapman@oracle.com>, Steve Ross-Talbot <steve@enigmatec.net>, "Champion, Mike" <Mike.Champion@SoftwareAG-USA.com>, public-ws-chor@w3.org
To: Assaf Arkin <arkin@intalio.com>
Message-Id: <CB0D048C-B8C6-11D7-8CCE-000393A3327C@mac.com>

No, that would be orchestration! ;-)

Frank

On Thursday, July 17, 2003, at 11:32  AM, Assaf Arkin wrote:

>
> So a Web Service Choreography does not choreograph Web services, it 
> choreographs agents?
>
> arkin
>
> Francis McCabe wrote:
>
>>
>> +1.
>>
>> Following the form of the WSA, we have agents that provide and 
>> request Web services. This is based on the intuition that a service 
>> is fundamentally about the potential for action, and that actors 
>> (computational and otherwise) are the entities that do the acting.
>>
>> Frank
>>
>> On Thursday, July 17, 2003, at 09:16  AM, Martin Chapman wrote:
>>
>>>
>>> I think there is a fundamental terminology issue here that needs to 
>>> be
>>> cleared up.
>>> An entity (avoiding any overloaded word) that sends a message to a 
>>> web
>>> service (and may expect a response depending on the wsdl) doesn not 
>>> iteslf
>>> have to be a web service. This is the most fundamental building 
>>> block.
>>> Furthermore this interaction supports an MEP (in soap teminology) and
>>> pattern (in wsd teminology).
>>> Perosnllay if we can not describe these meps in a choreography 
>>> language we
>>> have failed, and hence I do not think that mep choreogaprhy is any 
>>> different
>>> from web service choreography.
>>>
>>> Martin.
>>>
>>>
>>>
>>>> -----Original Message-----
>>>> From: public-ws-chor-request@w3.org
>>>> [mailto:public-ws-chor-request@w3.org]On Behalf Of Steve Ross-Talbot
>>>> Sent: Thursday, July 17, 2003 2:14 AM
>>>> To: Champion, Mike
>>>> Cc: public-ws-chor@w3.org
>>>> Subject: Grounding Choreographies (the atoms) - WAS Simple 
>>>> Choreography
>>>> composition suggestion
>>>>
>>>>
>>>>
>>>>    At the considerable risk of adding further confusion to the
>>>> discussion I would like to attempt to clarify what I said on the 
>>>> call
>>>> with respect to the grounding of a choroegraphy.
>>>>
>>>>
>>>>    Here is how I see it:
>>>>
>>>>    A "web service" choreography, as distinct from any other
>>>> choreography, is grounded to a minimum of two web services 
>>>> instances.
>>>> This may mean that the web services are the same web services but
>>>> different instance or it may mean that they are distinct 
>>>> (personally I
>>>> have a hard time seeing what they would be anything other than the
>>>> latter) such that I can observe a communication between them.
>>>>
>>>>    A communication is a minimum of a single message sent from one 
>>>> web
>>>> service to another web service.
>>>
>>>
>>>
>>>
>>>>
>>>>    It may be the case that in receiving or indeed sending a message 
>>>> the
>>>> sending web service and/or the receiving web service can be 
>>>> externally
>>>> observed to change their behaviour.
>>>>
>>>>    A "web service" choreography, as distinct from any other
>>>> choreography, is based on externally observable behaviour where this
>>>> behaviour is defined in terms of communications between web services
>>>> and externally observed behavioral changes of a web service.
>>>>
>>>>    For the avoidance of doubt, a Message Exchange Pattern (MEP) or 
>>>> any
>>>> mechanism that describes communication between two parties can be 
>>>> said
>>>> to be a choreography. But it cannot be said to be a "web service"
>>>> choreography.
>>>>
>>>>
>>>> Cheers
>>>>
>>>> Steve T
>>>>
>>>>
>>>> On Wednesday, July 16, 2003, at 02:57  pm, Champion, Mike wrote:
>>>>
>>>>>
>>>>>
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Fletcher, Tony [mailto:Tony.Fletcher@choreology.com]
>>>>>> Sent: Wednesday, July 16, 2003 9:12 AM
>>>>>> To: public-ws-chor@w3.org
>>>>>> Subject: FW: Simple Choreography composition suggestion
>>>>>>
>>>>>
>>>>>>
>>>>>> The point I disagree with is the notion that something is not a
>>>>>> Choreography if somewhere, at some level it involves 
>>>>>> 'orchestration'
>>>>>> within a single system.  If we accept this notion /
>>>>>> restriction it means
>>>>>> that you can only have Choreographies involving exactly two 
>>>>>> parties
>>>>>> where each party only plays a single role - we will not be
>>>>>> able to have
>>>>>> Choreographies with more than two parties / roles at all.
>>>>>
>>>>>
>>>>> That wasn't my intent, FWIW.  All sorts of compositions and
>>>>> decompositions
>>>>> can occur within a "choreography," but IMHO only those that 
>>>>> involve the
>>>>> globally visible shared state are in scope for the choreography
>>>>> description
>>>>> language we are developing.  The discussion yesterday got me
>>>>> re-thinking all
>>>>> sorts of things ... if the fundamental unit of a "choreography" is 
>>>>> a
>>>>> Web
>>>>> service invocation / MEP, then all sorts of implementation details 
>>>>> of
>>>>> the
>>>>> service that involved "orchestrated" interactions behind the 
>>>>> scenes are
>>>>> abstracted away, but if the fundamental unit is a message, then all
>>>>> those
>>>>> messages behind the scenes have to be accounted for somehow.  I'm 
>>>>> as
>>>>> confused as anyone at this point.
>>>>>
>>>>> By all means let's make sure that we don't box ourselves into a 
>>>>> corner
>>>>> based
>>>>> on some preliminary guesses about what terms mean!
>>>>>
>>>>>
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>>>>
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>>>>
>>>
>
>
> -- 
> "Those who can, do; those who can't, make screenshots"
>
> ----------------------------------------------------------------------
> Assaf Arkin                                          arkin@intalio.com
> Intalio Inc.                                           www.intalio.com
> The Business Process Management Company                 (650) 577 4700
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Received on Thursday, 17 July 2003 22:23:25 GMT

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